1. Field of the Invention
The invention relates to a marine streamer for use in seismic exploration, the streamer being suspended from buoyancy means to that it is maintained at a desired distance from the water surface.
2. Description of the Prior Art
In seismic exploration at sea one or a plurality of cables containing seismic energy sources is/are commonly towed behind a seagoing vessel. Pulses emitted by the energy sources are relfected from various layers of the sea floor and recorded by receivers or hydrophones which are also towed in the water and provided in special cables designated as streamers. The cables transmit the reflected and received signals, via various transmitting systems, to a recording unit, generally on board the towing vessel where the signals may be processed or stored in a suitable medium.
In connection with signal reception in the streamer, interference or errors may easily occur due to external circumstances or conditions inside the streamer or connected with transmission. Such interference may, e.g. be due to movement in the sea because of waves which may influence the results because the hydrophones move during reception and have no defined distance from the surface of the water or from the sea floor. These problems may be enhanced by exploration in shallow waters. One concept in this connection is to make the streamers heavier by being supported by buoyancy means which are provided at regular intervals on the streamer by the aid of sturdy suspension ropes. Even though this resulted in more steady movement of the streamer the buoyancy means still move and their forward movement in the water will also cause noise. A possible solution to this problem may be to guide the streamer by the aid of depth fins, so called "birds" which will keep the cable at a controlled depth below the water surface. This concept is, indeed a good solution, but the depth fins involve a complication and additional connection of electronics, also, the streamer must be specially built with properties adapted to this object.
In conection with seismic exploration in areas of shallow water, streamers with positive buoyancy, but provided with chains or the like sliding along the bottom, were used to maintain a defined distance from the bottom. This concept is, however, also burdened with obvious weak points since chains will make heavy noise and may, additionally, fasten on installations on the sea floor.